Passive Broadband Tracking may include triangulation or multilateration systems using time difference of arrival (TDOA) processing to track aircraft in local, regional and wide areas. These systems generally need pulse transmissions from the aircraft, which have sufficiently fast rise times in order to make a consistent time reference on the signal. Pulse transmission systems, having sufficiently fast rise times are generally higher frequency signals, L-band or above (generally higher than 900 MHz), with sufficient bandwidth to provide the fast rise time needed for passive broadband tracking. Signals with sufficient frequency and bandwidth include secondary surveillance radar systems (SSR), including Mode A, Mode C, Mode S, and ADS-B.
Companies fielding triangulation and/or multilateration systems for SSR include Sensis Corporation (www.sensis.com), ERA (www.era.cz) and Rannoch Corporation (www.rannoch.com), the respective websites thereof all of which are incorporated herein by reference.
While SSR signals are used for multilateration on the 1090 MHz frequency, there are others that use TDOA processing of other aircraft signals on different frequencies. One of these is the VERA-E system manufactured by ERA a.s., of the Czech Republic, as illustrated in FIGS. 1-3 and 5, taken from the website www.omnipol.cz, incorporated herein by reference. FIG. 1 illustrates a portable VERA-E passive sensor as set up in the field. FIG. 2 is a cutaway view of the VERA-E sensor, illustrating multiple antennas. FIG. 3 illustrates a VERA-E sensor as set up in the field, concealed by camouflage.
The VERA-E system may be used to track aircraft over wide areas using broadband methods. Essentially the broadband aspect is achieved by using a series of antennas and receiver systems interconnected as illustrated in FIG. 5. Each sub system handles a subset of frequencies in an overall range that includes from below 1 GHz to over 20 GHz.
A typical output from the VERA-E system is as follows:                Real time display        1-5 seconds update rate        Target/track ID        Coordinates x, y, (and z for 3D system)        Radar signal parameters (PRI, PW, CF, . . . ) and radar type/operation modes        SIF/IFF (3/A, C, 1, 2) modes        Barometric altitude (100 feet resolution) derived from Mode C reply        Mode S address (24 bits) and altitude from Mode S (25 feet resolution)        Mode 4 (IFF) flag        TACAN/DME channel/frequency and mode (X,Y)        GPS time        
Aircraft systems that can be tracked using this type of system include Joint Tactical Information Distribution System (JTIDS) and Distance Measuring Equipment (DME). A good description of JTIDS is found at http://en.wikipedia.org/wiki/JTIDS. incorporated herein by reference. The JTIDS system is an L-band TDMA network radio system used by the United States armed forces and their allies to support data communications needs, principally in the air and missile defense community. It provides high-jam-resistance, high-speed, crypto-secure computer-to-computer connectivity in support of every type of military platform from Air Force fighters to Navy submarines.
JTIDS is one of the family of radio equipment implementing Link 16, which is a highly-survivable radio communications design to meet the most stringent requirements of modern combat. Link 16 equipment has proven, in detailed field demonstrations as well as in the AWACS and JSTARS deployment in Desert Storm, the capability of basic Link 16 to exchange user data at 115 kilobit/s, error-correction-coded. (Compare this to typical tactical systems at 16 kilobit/s, which also have to accommodate overheads in excess of 50% to supply the same transmission reliability.) While principally a data network, Link 16 radios can provide high quality voice channels and navigation services as accurate as any in the inventory. Every Link 16 user can identify itself to other similarly equipped platforms at ranges well beyond what Mark XII IFF systems can provide. Additionally, Link 16-equipped platforms capable of identification through other means (such as radar and TENCAP blue force tracking) can pass that “indirect” identification data as part of its SA exchange.
According to an article appearing at http://www.sinodefence.com on Sep. 24, 2006, also incorporated herein by reference, there is another manufacturer of broadband multilateration systems, in addition to those previously enumerated. That article stated that during the 5th China International Electronic Exhibition (CIDEX) held in Beijing in Apr. 2006, 14th Institute of China Electronic Technology Corporation (CETC) revealed its YLC-20 passive surveillance radar system, which appears to be similar to the VERA-E.
The article went on to say, “the YLC-20 is a passive surveillance radar system similar to the VERA-E system developed by ERA of the Czech Republic. Based on the ‘Time Difference of Arrival Principle’, the system locates the source of signal position in two or three dimensions by solving for the mathematical intersection of multiple hyperbolas based on the Time Difference Of Arrival (TDOA) between the signal reception at multiple sensors. Using two hyperbolas (three receivers) the system can obtain 2D target position, while using at minimum three hyperboloids (four receivers) the system can achieve full 3D target locating. Higher accuracy can be achieved by using more receivers.”
Aircraft tracking may also be used as backup and validation for primary tracking systems. The use of triangulation or multilateration to provide an independent aircraft location is seen as a viable form of validation and back up to ADS-B. The FAA released two draft specifications relating to ADS-B and associated services in September 2006, listed below, both of which are incorporated herein by reference. These performance specifications do not require multilateration, but they provide performance requirements for the back up listed below and they provide guidance that multilateration may be used to provide the back up functions.                U.S. Department of Transportation, Federal Aviation Administration, Surveillance and Broadcast Services Program, Automatic Dependent Surveillance-Broadcast (ADS-B)/ADS-B Rebroadcast (ADS-R) Critical Services Specification, Draft, Version 0.30, 21 Sep. 2006.        U.S. Department of Transportation, Federal Aviation Administration, Surveillance and Broadcast Services Program, Traffic Information Service—Broadcast (TIS-B)/Flight Information Service—Broadcast (FIS-B), Essential Services Specification, Draft, Version 0.30, 21 Sep. 2006.        
These specifications provide draft requirements, subject to industry feedback, for independent validation performance as follows:                The ADS-B Service shall determine the validation status of at least 99% of aircraft/vehicles within 10 seconds of generation of the initial ADS-B Report for that aircraft/vehicle.        The ADS-B Service shall declare ADS-B data from an aircraft/vehicle to be valid if the independent measurement differs from the reported position by less than or equal to 1 NM.        The ADS-B Service shall declare ADS-B data from an aircraft/vehicle to be invalid if the independent measurement differs from the reported position by greater than 1 NM.        The probability of erroneously invalidating ADS-B data shall be defined.        
Thus, there clearly is a long felt need in the industry to employ ADS-B as a backup and/or validation for other tracking systems, as evidenced by the FAA draft specifications.
Surveillance sensors may be mounted in a number of locations. As noted in earlier filed applications by the assignee of the present application, such sensors may be located at an airport or off-site. Off-site installations may include, for example, cell phone towers or antenna placements. However, terrestrial-based forms of tracking traditionally suffer over large water areas, which constrains the positioning of sensors.
FIG. 4 illustrates a Prior Art six-meter NOMAD buoy with solar panels and communications equipment as used presently by the National Oceanic and Atmospheric Administration (NOAA). A selection of the type of buoys that may be used is provided on the website for the National Oceanic and Atmospheric Administration at:                www.ndbc.noaa.gov        www.ndbc.noaa.gov/mooredbuoy.shtml        www.ndbc.noaa.gov/images/Stations/6m.jpg        
all of which are incorporated herein by reference.
Different sized buoys for are used for deployment in various marine situations ranging from shallow water to deep water. Many of the buoys have power and communications available for installing equipment. According to NOAA, there are over 80 buoys deployed at various locations around the world. One example of such a buoy is the 6-meter diameter “NOMAD” buoy illustrated in FIG. 5. FIG. 6 illustrates an example of the range of available buoys used by NOAA.
In addition to sensors located on the ground or on marine vessels, sensors may also be located on aircraft or Unmanned Autonomous Vehicles (UAVs). Farmer et al., U.S. Pat. No. 7,123,169, issued Oct. 17, 2006 and incorporated herein by reference, entitled “Method and Apparatus for Collaborative Aggregate Situation Awareness” discloses gathering data from sensors located on multiple UAVs. The patent describes autonomous sensors that may proactively collect imagery on any vehicle that radiates a specific frequency. For example, an autonomous sensor may proactively collect imagery of ground moving target indicator (GMTI) tracks that are spaced closely together (which may mean an enemy convoy), or imagery of GMTI tracks that are moving toward friendly lines (which could be a sign of an enemy attack), or imagery of infrared (IR) hot spots detected with the IR sensor (that might be an enemy tank). An autonomous sensor may also listen for a signature sound or spore or scent, and fly upstream taking pictures of the source. The collaborative system can efficiently process requests and position the autonomous sensors at the right spot at the right time. This is achieved by the assignment of priorities to requesters, types of requests, and potential areas for requests.
Schneider, U.S. Pat. No. 6,910,657, issued Jun. 28, 2005 and incorporated herein by reference, discloses a system and method for locating a target and guiding a vehicle toward the target, describes time of arrival techniques for target location. Schneider states that time-of-arrival techniques are often employed to locate a radiating target, such as a Surface-to-Air Missile (SAM) battery. For example, three or more aircraft may time the arrival of electromagnetic energy emanating from the SAM battery. By measuring signal arrival time from the battery to the three or more aircraft, the location of the battery is determined. Clocks on the aircraft are synchronized via Global Positioning System (GPS) satellite clocks to enhance distance computation accuracy. Subsequently, a missile equipped with GPS/inertial guidance system is guided toward the measured position, i.e., GPS coordinates of the SAM battery.
The location of the missile during flight is measured by the on-board GPS/inertial guidance system to facilitate missile guidance. However, GPS guidance systems are susceptible to jamming, such as via jamming transmitters located near the target. In addition, GPS/inertial guidance systems often employ an expensive five element null-steering antenna. The null-steering antenna is capable of steering nulls to four jamming units. Consequently, use of more than four jamming units can successfully jam the accompanying GPS/inertial guidance system by overcoming the weak GPS signals from satellites.
Prior Art search and rescue operations for coastal applications have only recently implemented advanced technology to provide quick and accurate tracking capabilities for locating vessels in distress. In the Prior Art, a vessel in distress would attempt to contact the local Coast Guard on VHF channel 16, report their position, and wait for rescue. Unfortunately, since many mariners do not accurately know their position, such self-reporting often results in inaccurate data being transmitted, and as a result, delays in rescue attempts. In addition, false alarms by prank SOS announcements can waste valuable Coast Guard resources. Moreover, since channel 16 in many areas (e.g., Ft. Lauderdale) is rather busy, oftentimes Coast Guard personnel cannot hear broadcasts from vessels in distress, as the signals may be “stepped on” by local recreational boaters.
Traditional triangulation techniques may be utilized to locate mariners in distress, by measuring radio signal direction from at least two on-shore locations, and then triangulating an off-shore position. However, such a technique requires that the radio signal be on long enough for the on-shore receivers to fix on the signal, and moreover that the signal is not interrupted by other radio traffic. Weak or intermittent signals, which often occur when a vessel is in distress (e.g., low or no battery power, engine room awash, or the like), or when the person in distress is using a hand-held portable radio, may be difficult to track.
To correct some of these problems, the U.S. Coast Guard offers MF/HF radiotelephone service to mariners as part of the Global Marine Distress and Safety System. This service, called digital selective calling (DSC), allows mariners to instantly send an automatically formatted a distress alert to the Coast Guard or other rescue authority anywhere in the world. Digital selective calling also allows mariners to initiate or receive distress, urgency, safety and routine radiotelephone calls to or from any similarly equipped vessel or shore station, without requiring either party to be near a radio loudspeaker. All new VHF and HF radiotelephones have DSC capability.
On Feb. 1, 1999, the Safety of Life at Sea (SOLAS) Convention, a treaty document, required all passenger ships and most other ships 300 grt and larger on international voyages, including all cargo ships, to carry DSC-equipped radios. Ships were allowed to turn off their 2182 kHz radio listening watch on that date. The International Maritime Organization has postponed indefinitely plans to suspend this VHF watch on ships. It had originally planned to suspend this watch on Feb. 1, 2005.
Because of the safety problems that lack of communications interoperability would cause between SOLAS-regulated vessels (mostly cargo ships) and other vessels (recreational boaters, commercial fishing vessels, etc.), the Coast Guard petitioned the Federal Communications Commission in 1992 to require all marine radios made or sold in the U.S. to have a DSC capability. The Coast Guard had also asked the Radio Technical Commission for Maritime Services (RTCM), a non-profit professional organization, to develop a standard, which would allow incorporation of DSC in a marine radio without affecting the low-end market price of that radio for recreational boaters. The FCC solicited comments on that petition in 1992 and 1993, and prepared a Notice of Proposed Rulemaking on that and other maritime radiocommunications matters in early 1994. The FCC requested comments concerning that rulemaking from May to November 1995. On 27 Jun. 1997, the FCC adopted a Report and Order requiring radios type accepted on or after 17 Jun. 1999 to include this minimum DSC capability.
The International Telecommunications Union Sector for Radiocommunications has indicated that excessive test calls on MF/HF DSC distress and safety frequencies are overloading the system to the point where interference to distress and safety calls has become a cause for concern. To minimize possible interference, live testing on DSC distress and safety frequencies with coast stations should be limited to once a week as recommended by the International Marine Organization.
To date, only a limited number of DSC receivers have been installed by the Coast Guard. Many USCG Group offices operate MF DSC on a trial basis. The Coast Guard plans to declare a Sea Area A2 (have an operational MF DSC service) for the Contiguous US coast and Hawaii. The US currently does not have a declared Sea Area A2.
All DSC-equipped radios, and most GPS receivers, have an NMEA 0183 two-wire data interface connector. That NMEA interface allows any model of GPS to be successfully interconnected to any model of radio, regardless of manufacture. Although NMEA has no standard for the type of connector used, many if not most DSC and GPS receiver manufactures use bare wire connections. These wires are simply connected between the radio and the GPS by twisting the wires (preferably solder) and tape (preferably waterproof heat shrink tubing).
In operation, the boater presses a button (usually mounted on the back of the microphone, underneath a safety cover) to declare a distress condition. The DSC-equipped VHF radio then transmits the GPS-based location of the vessel digitally to a DSC-equipped receiver station, and rescue personnel can be dispatched to the distress site.
Thus, the DSC system suffers from a number of systemic and implementation problems. Many boaters have older radios without DSC capability, and it will be several years, if not decades, before all of these older-style radios are purged from the marketplace, as many recreational boaters do not see implementing DSC as a priority, and for many boaters, the cost of installing a new DSC radio is deemed excessive. In addition, many older GPS systems do not have the two-wire interface needed to connect to a DSC-compatible radio. Further, many boaters have not taken the time to make such connections, and, as noted above, since no standard connector exists, many connections are bare-wire type, which may not be reliable in a salt-water environment, or may be connected improperly, or become disconnected due to vibration and the like.
Even if connected, there is no guarantee the system will work. Extensive testing if DSC signals, as previously noted, has resulted in clogging of the DSC system, so boaters are not encouraged to test their system to insure it works properly. Moreover, boaters are encouraged to register their DSC-equipped vessels with the Coast Guard, such that a DSC emergency signal can be matched to a boating database to identify the vessel in distress. Most recreational boaters are unaware of this registration process, and few take advantage of it.
As a result, the DSC system suffers from the same implementation problems as many retrofit aircraft systems, such as collision avoidance (e.g., TCAS) or terrain sensing systems. These systems rely upon individual vehicle owners to install and maintain equipment to make the system operational. The system also will take time for such equipment to make its way though the existing vehicle inventory. Aircraft owners, may be required to install such equipment, and the safety concerns may compel many owners to install such equipment, even if not required to do so. However, unlike aircraft owners, most recreational boating owners are more lax about installation and maintenance of such equipment, and thus implementing and keeping installed DSC systems operational is more of a problem. A better solution would be to provide a vessel tracking system, which does not require recreational boaters to install and maintain new equipment, or one that allows for less complex equipment to be used, or to provide such a vessel tracking system as an adjunct to the DSC system.
In addition to the applications noted herein, multilateration and triangulation systems may be used for correlation with vibration, noise, audio, video, and other Information. Other sources of information that may be correlated with aircraft or vehicle track information include audio and video data. Currently there are many systems that correlate this information used for environmental management including those implemented by Rannoch Corporation (www.rannoch.com), Lochard (www.lochard.com), Bruel and Kjaer (www.bksv.com), BAE Systems and others, the respective websites thereof all being incorporated herein by reference. These systems may correlate the data in order to determine and identify which specific aircraft generated noise events or noise levels. Vibration monitoring may also be employed by these systems to track lower frequency events such as engine run-ups at airports. Although it has been discussed in the industry, airport noise monitoring systems have not generally employed methods to analyze the spectral content of aircraft noise for the purposes of classification (e.g., to distinguish between a jet or a turboprop).
In the example illustrated in FIG. 7 is from the BAE TAMIS™ product to compute the point of closest approach of an aircraft. PCA statistics include:                Slant distance,        Ground distance,        Aircraft position and altitude,        Date and time of the PCA,        Elevation angle from the PCA center point to the flight        Aircraft ground heading.        
FIG. 8 illustrates a flight track that is selected from point of closest approach. FIGS. 9 and 10 illustrate a typical NOMS layout where the aircraft tracks are illustrated on a GIS map along with the locations of noise monitors. FIG. 10 illustrates the actual recorded noise level at each of the monitors on the GIS map. FIG. 11 illustrates a typical noise event for an aircraft as a Single Event Level or “SEL.”
Primary radar is, of course, an active element, and if used as part of a surveillance configuration it is no longer covert. However, there are many opportunities in fielding passive systems to integrate feeds from existing radars to improve overall surveillance. Radar types range from long range systems covering several hundred miles to high frequency systems that cover only a few hundred meters, including:                Long range ASRS-4 built by Westinghouse/Northrop Grumman (www.ngc.com)        Terminal ASR-8, 9, 11, 12 built by Raytheon (www.raytheon.com) and Northrop Grumman        Surface Ku band radar by Cardion/Northrop Grumman        Surface X band radars including those built by Terma (www.terma.com), Sensis (www.sensis.com), and Thales (www.thalesatm.com)        Lower range, higher frequency radar such as the Tarsier™ by QinetiQ and the 77 GHz radar produced by Navtech (www.nav-tech.com).        
Thus, it also remains a requirement in the art to fuse data from various surveillance sources, including primary and secondary radars, passive tracking systems, and the like, to create a robust and verified flight track or vehicle track, with redundant data inputs.